In traffic control applications, it is often desirable to detect traffic incidents that cause a disruption in the flow of traffic. Conventional traffic management systems use sensors that monitor the presence and speed of vehicles without individually identifying each vehicle. Such systems rely on gathering data from traffic helicopters, camera systems, and sensors to detect the presence of a vehicle. One such system includes an induction loop buried in a roadway.
Conventional systems typically use incident detection algorithms that process the sensor data and declare when an incident has occurred. One such algorithm includes detecting a queue of vehicles that forms because a traffic incident causes a backup in a roadway. There is a need to minimize the rate of false alarms while attempting to quickly detect the formation of a queue. A false alarm occurs when a queue is incorrectly detected and an incident is declared by the algorithm but has not in fact occurred. One solution to this problem requires close sensor spacing (about one km) to quickly detect that a queue is forming. Closely deployed sensors are expensive in terms of infrastructure and maintenance costs.
There have been attempts to monitor the time required for a small set of vehicles to travel various sections of highway. These vehicles have special instrumentation that allows the vehicles to record time and location while traveling on the roadway. These attempts have mainly been for traffic reporting purposes rather than incident detection.
Conventional traffic control systems require several operators and expensive remote control cameras with zoom, pan and tilt features. These systems can miss traffic problems on sections without cameras. In addition there is no early warning of traffic incidents. Other industry standard algorithms use data collected by induction loop sensors that can measure the number of vehicles and speeds of the vehicles. These algorithms wait for queues to build up before detecting problems. These systems require closely spaced sensors because queues can build up anywhere on the roadway and information about the travel time of individual vehicles is not being collected and processed.
U.S. Pat. No. 5,696,503 entitled “Wide Area Traffic Surveillance Using a Multisensor Tracking System,” and assigned to Condition Monitoring Systems, Inc, describes a wide area traffic surveillance using a multi-sensor tracking system. This system attempts to track individual vehicles within a sensor's field of view in a manner similar to an air traffic control radar system.
In order to detect incidents anywhere on the road within, for example five minutes, sensor spacing cannot exceed the size of the queue that develops five minutes after an incident. If the sensors were widely spaced, a conventional algorithm might not detect a queue build up for several minutes because the sensor might be located a distance, equal to traveling five minutes at an average speed, before the occurrence of an incident. Where the traffic flow is light, an incident would only cause the formation of a short queue of vehicles. A conventional system would require sensors to be spaced less than 500 meters apart to detect the short queue within five minutes.
By rapidly detecting traffic incidents on a roadway, emergency personnel can be dispatched to minimize the time that traffic lanes are blocked. For a roadway operating near capacity, it can take longer for a queue to clear than the time that the incident actually blocks traffic. It is therefore important to reduce the potential backlog of traffic by rapid detection.